A conventional scroll type compressor has a movable scroll and a stationary scroll each of which has a round base plate provided more than one spirally shaped scroll blade. The movable scroll and the stationary scroll are engaged which one another to form a closed working chamber. The movable scroll is prevented from rotating on its own axis by anti-rotation mechanism, and a shaft having an eccentric portion makes the movable scroll orbit so that the volume of the working chamber is decreased to achieve a pumping operation.
In more detail, as shown in U.S. Pat. No. 4,650,405, the eccentric portion of the shaft is engaged with the round base plate of the movable scroll at the center portion of the round base plate and the anti-rotation mechanism is provided around the engaging portion of the eccentric portion and the round base plate. When the engaging portion mechanism, the anti-rotation mechanism does not work, the pumping operation is not achieved properly. To avoid this situation, an end portion of the driving shaft is disposed at the center portion of a housing in which the movable and stationary scroll are provided. That causes restrictions on designing and positioning of the compressor in a car, and the shaft to support the movable scroll disadvantageously becomes a cantilever. The anti-rotation mechanism affects the scroll-type compressor in its consumption power, efficiency and reliability because the orbital radius of the movable scroll depends on the anti-rotation mechanism.
The conventional anti-rotation mechanism is described in Japanese Patent Unexamined (Kokai) Publication No. 55-155916. In such anti-rotation mechanism, the housing and movable scroll have a plurality of grooves on its contacting surface, and balls or rollers are provided in the grooves.
In the anti-rotation mechanism using balls, each ball is in contact with a groove at one point and the load applied to each of balls becomes large. In order to disperse the load applied to each of the balls, it is necessary to increase the number of balls. When the number of balls increases, the diameter of the compressor increases. Because the orbital diameter of the movable scroll depends on the diameter of the groove, high precision of the groove driving production is required and the cost increases. When the production precision of the groove is low, the movable scroll and the stationary scroll come into contact with one another so that the consumption power increases and heat is generated, or the clearance between the movable scroll and the stationary scroll becomes large so that the efficiency of the compressor is decreased.
In order to orbit one of the scrolls, it is necessary to provide at least two balances which rotate while keeping a certain phase difference relative to the movable scroll. The three balances including the movable scroll keep the balance; however, these balancers disadvantageously increase the number of parts and weight of the compressor and its cost.